In accordance with a rapid spread of information relevant apparatuses and communication apparatuses such as a personal computer, a video camera and a portable telephone in recent years, the development of a battery to be utilized as a power source thereof has been emphasized. The development of a high-output and high-capacity battery for an electric automobile or a hybrid automobile has been advanced also in the automobile industry. A lithium battery has been presently attracted attention from the viewpoint of a high energy density among various kinds of batteries.
Liquid electrolyte containing a flammable organic solvent is used for a presently commercialized lithium battery, so that the installation of a safety device for restraining temperature rise during a short circuit and the improvement in structure and material for preventing the short circuit are necessary therefor. On the contrary, a lithium battery all-solidified by replacing the liquid electrolyte with a solid electrolyte layer is conceived to intend the simplification of the safety device and be excellent in production cost and productivity for the reason that the flammable organic solvent is not used in the battery.
A Li—La—Ti—O based solid electrolyte material (LLT) has been known as a solid electrolyte material used for an all solid state lithium battery. For example, in Non Patent Literature 1, an amorphous thin membrane of Li0.5La0.5TiO3 is disclosed. The composition of this thin membrane corresponds to the case of x=0.17 in a general formula: Li3xLa2/3−xTiO3. Also, in Patent Literature 1, a solid electrolyte membrane having lithium ion conductivity is disclosed, which has a composition of LaXLiYTiZO3 (0.4≦X≦0.6, 0.4≦Y≦0.6, 0.8≦Z≦1.2, Y<X) and an amorphous structure. This composition range differs completely from a composition range of Li3xLa2/3−xTiO3.
Also, in Patent Literature 2, a solid electrolyte layer composed of a solid electrolyte including a complex oxide containing Li, La and Ti is disclosed, in which the solid electrolyte layer comprises an amorphous layer, a crystalline layer, and a lattice defect layer. In addition, in Patent Literature 2, it is described that the composition of a solid electrolyte material is preferably La2/3−xLi3xTiO3 (0.03≦x≦0.167). This solid electrolyte material is synthesized by performing planetary ball milling and burning, and corresponds to the so-called bulk body, and is not a thin membrane.